Electrosensitive Protective Equipment (ESPE) is well-known and widely used in industrial settings to protect operators of hazardous equipment from injury. ESPE devices typically have a sensing function, a control or monitoring function, and an output signal switching function. The sensing function typically collects data from, for example, a defined safety zone surrounding dangerous equipment. The safety zone may be a line, an area, or a volume, depending on the sensing technology used. The control function monitors the sensing function. When the control function determines that the sensor data provided by the sensing function corresponds to an intrusion into the safety zone, an output signal is produced to sound an alarm, deactivate the hazardous equipment, or perform some other precautionary measure.
A variety of ESPE devices are currently commercially available, including single beam photodetectors, light curtains, laser scanners, safety mats and others. Single beam photodetectors typically use a single light source and light detector to provide some level of access monitoring. When an object moves between the light source and the light detector, the light beam extending therebetween is interrupted, which then triggers a safety violation. A limitation of single beam photodetector systems is that only limited access control and typically no presence sensing is provided. Another limitation is that to change the location, shape or size of the safety zone, the light source and/or light detector must typically be physically moved.
Light curtain systems are similar to single beam photodetector systems, except a linear array of light emitter/light detector pairs are provided. The light emitter/light detector pairs are mounted in a pair of spaced enclosures. The array of light emitters produce a “light curtain” that extends to the corresponding light detectors. When the light curtain is interrupted by an object, a safety violation is triggered. The resolution (size of object detected) typically depends on the spacing of the light beams. Light curtain systems can provide some level of access control when mounted vertically, and some level of presence monitoring when mounted horizontally. However, a limitation of some light curtain systems is that they are relatively expensive and complex. Another limitation is that variations in the size and shape of the safety area may be restricted, and the spaced enclosures must typically be physically moved to change the configuration of the safety zone to be monitored.
Laser scanner system typically include a rotating laser emitter/detector, which scans a plane and measures the distance to the nearest object in any direction by monitoring the reflection of the beam. This type of device can provide some level of presence monitoring along a horizontal plane. It may also be mounted vertically to provide some level of access monitoring, similar to the light curtain systems discussed above. A limitation of laser scanner systems is that they use complex mechanical components, such as rotating heads, which can requiring periodic and precise alignment. While the region to be monitored may be redefined using configuration software, its shape is often limited by the line-of-sight of the laser. Also, the response time is limited by the need to rotate the laser beam, and the sensitivity may be limited by air pollution in an industrial environment.
Finally, safety mat systems have been used to provide presence monitoring by detecting physical contact with a floor mat/sensor. Its robustness is limited by the need for physical contact with the floor mat for detection, which can be problematic in the often harsh environment of the factory floor. Safety mat systems typically cannot monitor large areas unless a number of mats are connected together. Finally, and like the single beam photodetector and light curtain systems described above, the safety mats must typically be physically moved to change the configuration of the safety zone to be monitored.